WASHINGTON, Jan 4 (Reuters) - A U.S. judge on Wednesday denied Volkswagen AG and its former chief executive Martin Winterkorn's requests to have an investor lawsuit dismissed in California over its "Dieselgate" emissions scandal.

In a 41-page ruling, U.S. District Judge Charles Breyer also rejected a request by VW brand chief Herbert Diess to have the proposed securities fraud lawsuits tossed out of a California court. The investors suing are mostly U.S. municipal pension funds that invested in VW through American Depositary Receipts.

Volkswagen argued that German courts were the proper place for investor lawsuits.

(Reporting by David Shepardson; Editing by Bernard Orr)